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Space Shuttle Discovery Sonic Boom Recorded

by the Southern California Seismic Network

Among the earthquakes and mining blasts recorded daily by the SCSN, there are also occasional sonic booms.  The best examples seem to come from the space shuttle arriving at Edwards Air Force Base, as the Discovery did very early this morning.  The sonic boom is a shock wave in the air produced when the front end and then the back end of the spacecraft slow from supersonic to subsonic speeds, hence the double boom that people (and seismometers) often notice.  When the air wave hits the ground, some of the energy propagates into the ground, to be recorded by our seismometers.

The recordings shown here are this morning's boom just as the SCSN seismic analysts see it.  There are two obvious differences between these recordings and the usual earthquake recordings.  First, although there may be two pulses, due to the shock generated at the front end and the back end of the shuttle, they are both shock waves in the air, not P and S waves.  Therefore they do not get farther apart in time at more distant stations.  The second obvious difference is the large time delay between the arrivals at the various seismic stations.  This occurs because the wave is propagating at the speed of sound in the air (1100 feet per second or 0.37 km per second), much slower than the P and S velocities in the ground (2 to 8 km per second depending on the rock layer).

The waveforms are available for download via STP by clicking here.

This morning's sonic boom also has its own entry in the "Did You Feel It?" (CIIM - Community Internet Intensity Map). If you experienced the sonic boom, and would like to contribute to the data collected, please click here.

Kate Hutton, Staff Seismologist

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